The present invention relates generally to a pressure regulating device for use in an automatic transmission and more particularly to a fluid pressure regulating device which is adapted to feed fluid discharged from a hydraulic pump into a torque convertor and particular portions of the transmission for lubrication.
The pressure of fluid discharged from the pump is regulated to a line pressure commensurate with vehicle speed and engine output through a first pressure regulating valve. The pressurized fluid is supplied to each of a plurality of hydraulic power cylinders. Pressure of excess fluid supplied to the hydraulic control system from the first pressure regulating valve is regulated commensurate with the vehicle speed and engine output through a second pressure regulating valve. The pressurized fluid from the second pressure regulating valve is applied to the torque convertor and selected portions of the transmission for lubrication. The pressurized fluid supplied to the torque convertor circulates in the torque convertor and is discharged from the torque convertor through a return passage, an intermediate passage of the second pressure regulating valve and optionally through a cooler to return to a fluid reservoir.
In the prior art, this second pressure regulating valve is adapted to close the return passage from the torque convertor to the reservoir so that when the engine is stopped, the oil pressure in the torque convertor is not discharged from the torque convertor to the cooler and the oil reservoir.
When an automatic transmission having such a pressure regulating device is installed on an automotive vehicle having an engine of increased capacity, because line pressure is set higher in accordance with the increased capacity, the second pressure regulating valve receives a diminished quantity of excess fluid from the first pressure regulating valve which causes diminished functional performance by the second pressure regulating valve. Particularly, upon running of the automotive vehicle at low speed, the second pressure regulating valve does not perform its pressure regulating function and excess fluid is introduced directly into the torque convertor and the respective portions of the transmission requiring lubrication. As a result, the return passage from the torque convertor by way of the second pressure regulating valve is closed. By closing of this return passage, no circulation of fluid is caused in the torque convertor, thereby overheating the fluid within the torque convertor, increasing leakage and decreasing the quantity of fluid discharged from the pump.
In order to prevent such overheating of fluid or oil in larger capacity engines, a pump having an increased pumping capacity is required. Use of a larger pump uses more engine power and engine output, thereby raising operational costs and requiring modification of engine parts. Accordingly, such a solution, that is, installing such an enlarged capacity pump is not preferable on the automatic transmission.
What is needed is a pressure regulating device for use in an automatic transmission on larger capacity engines which is of normal capacity and does not allow overheating of the fluid in the torque convertor.